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The Polymerase Chain Reaction (PCR) was used to detect the qacA gene which encodes antiseptic resistance in 186 clinical isolates of Staphylococcus aureus. The results were compared with those obtained by MIC determination of 4 antiseptics (benzalkonium chloride, hexamidine, chlorhexidine, acriflavine) and for ethidium bromide. The qacA gene was not detected among the 32 susceptible S. aureus strains, but was found in the 70 (85%) of the 82 S. aureus strains resistant to all 5 antiseptics. The gene was also detected in 70 (45%) of the 154 remaining strains that were resistant to at least one antiseptic.

A flocculating strain of Saccharomyces diastaticus NRRL2416 was isolated after ethidium bromide mutagenesis and density gradient separation. Flocculation did not change the general characteristics of the strain. Flocculation was better on maltodextrin-containing media than on others. It was found to be calcium-dependent and sensitive to growth conditions. The deflocculating effects of some sugars suggested that mannose may be involved in the mechanism of flocculation, as for strains of the FLO1 phenotypic group.

Nucleoid sedimentation analysis was applied to the study of DNA supercoiling repair in cultured FR 3T3 fibroblasts exposed to low doses of fast neutrons or gamma-rays. Supercoiling was fully restored in both instances upon post-irradiation at 37 degrees C, but the rate of repair of neutron-induced lesions was lower than that for gamma-rays. Non-repairable breaks were not evidenced at the neutral pH used. We suggest that the non-repairable alkali-labile sites evidenced by others in neutron-irradiated DNA do not prevent strand break rejoining and subsequent recovery of the tertiary DNA structure.

A strain of C. perfringens type A, isolated from a patient, was found to be resistant to four antibiotics: tetracycline (Tet), chloramphénicol (Chl), erythromycin (Ero) and clindamycin (Cli). Clones resistant to only two drugs (Tet-Chl or Ero-Cli), or sensitive to all drugs were found in cultures of the wild-type strain treated by acridine dyes or ethidium bromide. DNA analysis by equilibrium centrifugation confirmed that the original strain contains two resistance plasmids, one called Rip 401 (Tet-Chl) and the other Rip 402 (Ero-Cli), which represent respectively 1.8 +/- 0.2% and 2.3 +/- 0.2% of the total amount of DNA in this strain of Cl. perfrigens.

The induction of the mitochondrial 'petite' mutation (rho-) in haploid yeast (Saccharomyces cerevisiae) by ethidium bromide is reduced or even abolished if cells are also treated with the gas phase of cigarette smoke. This is observed not only in the case of simultaneous treatments but also when the two drugs are applied in succession.